1. Field of The Invention
The present invention relates to a system for automatically controlling operations of construction vehicles, and more particularly to an automatic system for controlling relative operational velocity of actuators of such construction vehicles which is capable of calculating, during a half cycle of an operation, relative operational velocity ratio between actuators on the basis of displacements of the actuators and calculating the electric control currents on the basis of the relative operational velocity ratio, then automatically controls, during the other half cycle of the operation, the flow rate of a hydraulic fluid outputted from main hydraulic pumps by using the electric control currents.
2. Description of The Invention
Conventionally, it is well known that hydraulic construction vehicles, such as an excavator, are useful industrial machines. The conventional construction vehicles are generally provided with a plurality of operational members which practically carry out desired operations, several actuators for actuating the operational members, a driving engine for supplying the driving power, hydraulic pumps for supplying compressed hydraulic fluid for the actuators upon receiving the driving power from the engine, proportional valves for controlling wobbling angles of wobble plates of the hydraulic pumps, directional control valves each adapted for controlling a flow rate and a flowing direction of the hydraulic fluid, a plurality of positional sensors for sensing displacements of the actuators, control levers/pedals being manipulated by the operator in order to instruct a desired operation, an electronic controller for controlling the operations of the actuators upon receiving manipulation signals from the control levers/pedals.
The actuators of the construction vehicles are controlled by virtue of operator's manipulation for the control levers/pedals so that the actuators efficiently actuates the operational members in order to carry out several operations such as an excavating operation, a surface finishing operation, a loading operation and the like.
During an operation of the construction vehicles, several actuators of the vehicles generally need to be operated by the operator at the same time. Here, each control lever is generally used for controlling two actuators. For example, in a loading operation by using an excavator, it is necessary that two of four actuators, that is, a swing motor and a boom cylinder or a bucket cylinder and a dipper stick cylinder are operated at the same time. In addition, each two actuators are simultaneously operated by means of a manipulation for a control lever. Thus, the operator has to manipulate two control levers at the same time by using both hands in order to operate the two actuators. In result, the known construction vehicles have disadvantage in that a manipulation for a control lever has to synchronize with other manipulation for another control lever so that the synchronizing manipulation for the control levers imposes a burden for the operator regardless of skill of the operator, thus causes the operational velocity of the construction vehicle to be slow, thereby resulting in deteriorating the operational effect of the construction vehicle.
In an effort for solving the above problem, there has been proposed construction vehicles which each is provided with an operational velocity setting device electrically connected to the controller in order to set a relative operational velocity ratio between two actuators and output an electric signal corresponding to the velocity ratio having been set by the setting device to the controller.
For example, The Japanese Patent Publication No. Sho. 63-93,936 discloses a representative example of the above-mentioned type of construction vehicle, that is, an excavator which is provided with a velocity setting device which automatically controls a relative operational velocity ratio between two actuators, as shown in FIG. 1.
FIG. 1 is a schematic view showing a relative connection between a hydraulic circuit and an electronic control circuit including a device for setting an operational velocity ratio between a swing motor and a boom cylinder of the excavator in accordance with the prior art.
As shown in the drawing, the excavator is provided with a driving engine 1 which is connected to a pair of hydraulic pumps, that is, first and second main pumps 2 and 3. The first main pump 2 is connected to a directional control valve 4 which is adapted for controlling flow rate and flowing direction of the hydraulic fluid for the swing motor 6, while the second main pump 3 is connected to a directional control valve 5 which is adapted for controlling flow rate and flowing direction of the hydraulic fluid for the boom cylinder 7. In addition, the directional control valves 4 and 5 each is electrically connected to an output port of an electronic controller 8. The input ports of the controller 8 is electrically connected to a boom cylinder control lever 9, a swing motor control lever 10, an automatic select switch 11 and an operational velocity setting device 12.
In operation, upon setting each desired operational velocity of the swing motor 6 and the boom cylinder 7 by using the operational velocity setting device 12 in order to predetermine a desired operational velocity ratio therebetween, the controller 8 controls the directional control valves 4 and 5 in order to cause the swing motor 6 and the boom cylinder 7 to be actuated at the operational velocity ratio set by the velocity setting device 12. Thus, if the operator simply manipulates the boom cylinder control lever 9 and the swing motor control lever 10 in the maximum, respectively, the controller 8 outputs control current signals to the directional control valves 4 and 5 in order to cause the swing motor 6 and the boom cylinder 7 to be automatically actuated at the operational velocity ratio. Accordingly in an operation, such as an excavating operation, the operator can so easily manipulate the control levers 9 and 10 for the actuators at the same time that he simply manipulates the control levers 9 and 10 in order to control the dipper stick cylinder and the bucket cylinder with disregarding the manipulation for the control levers 9 and 10 for controlling the swing motor 6 and the boom cylinder 7.
However, in the above excavator provided with the velocity setting device 12, the operator has to set by experience the operational velocity ratio between two actuators, thereby inducing a disadvantage in that the operator should be enough skilled to reliably set the operational velocity ratio between two actuators. Furthermore, the operator always sets new operational velocity ratio between two actuators when the operational condition changes, thereby inducing another disadvantage in that the operator is troubled with the repeated setting for the velocity ratio.